Parties like the AfD and the Greens have grown in national support following Germany’s 2017 general election, as support for the major centre parties has waned.

And with the CDU’s party conference scheduled for December, Mrs Merkel could lose her leadership re-election bid.

She has said previously she could not continue as chancellor – a position she has held for 13 years – were she to lose that role.

A big blow for Angela Merkel

By Jenny Hill, BBC’s Berlin correspondent

It’s been a bruising evening for Angela Merkel.

Her party has lost significant support in the wealthy state of Hesse, home to the financial centre of Frankfurt.

The result is widely interpreted not as a rejection of local politicians but rather a protest against Mrs Merkel’s unhappy coalition government in Berlin.

The losses are undoubtedly ammunition for critics in her party who want rid of Mrs Merkel. But she may face a more immediate problem.

Her Social Democrat coalition partners are in electoral freefall, haemorrhaging support at federal level.

The SPD’s poor performance tonight in Hesse follows a drubbing in Bavaria two weeks ago. Many in the party blame the controversial coalition with Mrs Merkel’s conservatives. The SPD’s leaders may decide to pull out of the alliance and bring down her fragile government.

Germans are calling this a ‘schicksalswahl’, or vote of destiny. It may yet seal the fate of this country’s government – and perhaps even its leader.